Nagasi succeeded to unite fragmented Amhara districts in Shewa, and launched several wars of reconquest of Shewan territories against his Oromo enemies.
[2] In the 16th century, Christian Abyssinia was devastated after the conclusion of the long running Ethiopian–Adal War, which culminated in the defeat of the Adal Sultanate and their Ottomans backers during the Battle of Wayna Daga.
In this vulnerable state, a new threat emerged from the south, the Oromos migrated northwards and began a series of conquests into Shewa, Gurage, Welega, Bete Amhara and other areas.
Shewa was almost completely lost to the Imperial authority by the end of Sarsa Dengel's reign, and de facto separated from the Gondarine kingdom during most of the 17th century.
There are several traditions about Nagasi's lineage; the official account from the Shewan dynasty (as told by Serta Wold, councillor of Negus Sahle Selassie in the 1830's and 1840's) is that he was a male line descendant of the Solomonic Emperors through abeto Yaqob, the fourth son of Lebna Dengel, who remained in Shewa.
His mother, Senebeit, was related to the monarchs residing in Gondar through her father Ras Faris of Dair, "who with many other followers of Emperor Susenyos escaped into Menz."
[9][10] As a young man, Nagasi showed outstanding valor and skills at arms in a series of battles with the neighbouring Amhara families.
According to Donald Levine, Nagasi was buried in the church Fit Abbo, "where his grave -- as well as the field he camped on, Nagassi Meda -- remain objects of historical interest today.